Lines from the song

      Lithium, don't want to lock me up inside.
(DOESN'T WANT TO LOCK UP THE PART OF HER WHICH IS SADNESS)

Lithium, don't want to forget how it feels without...
(DOESN'T WANT TO FORGET THE SAD PART OF HER)

Can't break free until I let it go.
(SHE CANT BE HAPPY TILL SHE LETS GO OF ALL THE SADNESS)

Drown my will to fly.
(SHE IS RESISTING THE URGE TO BECOME HAPPY)